1.  Marriage Record:

2.  1880 Census Every-Name-Index/Images (online at Ancestry.com, Image #3 of 18 — indexed "D... Holt"):  Whitman Co., WA, Roll T9_1398, p. 375C, PN 3, SD, ED 58, enumerated 4 Jun 1880, official enumeration date 1 Jun 1880 (extracted by Diana Gale Matthiesen):

1880:  for an explanation of the column headings, please see What the Numbers in the Federal Census Mean (missing columns contained no data).

1

2

3

4

5

6

7

8

9

10

13

24

25

26

22

24

Holt Dcke?

W

M

26

/

Farmer

SC

NC

SC

____ Nancy H

W

F

18

Wife

/

Keeping house

OR

IL

IL

____ Della

W

F

6/12

Nov

Dau

/

WA Ter

SC

OR

As far as we know, Dionysius's father was born in Tennessee.  Listed next to Dionysius's brother, James B. HOLT. 

3.  1890 Census:  the 1890 Census Population Schedules were destroyed.

4a.  1900 Census Index/Images (online at Genealogy.com, Image #11 of 19 — indexed "Dionysin M. Holt"):  Palouse City, Whitman Co., WA, Roll 1753 (Book 2), p. 147A, SN 6B, SD 2, ED 98, enumerated 12 Jun 1900, official enumeration date 1 Jun 1900 (extracted by Diana Gale Matthiesen):

1900:  for an explanation of the column headings, please see What the Numbers in the Federal Census Mean (missing columns contained no data).
1	2	3	4	5	6	7	8	9	10	13	14	15	19	20	22	23	24	25	27
147	147	Holt Dionysius M	Head	W	M	Nov 1854	45	M	21	SC	NC	SC	Dry Goods Salesman	0	Y	Y	Y	R	H

4b.  1900 Census Index/Images (online at Genealogy.com, Image #5 of 17):  South Pullman (Pct. No. 41), Whitman Co., WA, Roll 1754 (Book 1), p. 237A, SN 8, SD 2, ED 104, enumerated 7 Jun 1900, official enumeration date 1 Jun 1900 (extracted by Diana Gale Matthiesen):

1900:  for an explanation of the column headings, please see What the Numbers in the Federal Census Mean (missing columns contained no data).

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

19

20

21

22

23

24

25

27

157

158

Holt Mammie H

Head

W

F

Nov 1861

38

M

21

5

5

OR

Unk

Unk

Y

Y

Y

R

H

____ Della

Dau

W

F

Nov 1879

20

S

WA

SC

OR

Teacher

2

Y

Y

Y

____ Helen L

Dau

W

F

Aug 1884

15

S

WA

SC

OR

At School

4

Y

Y

Y

____ Zena A

Dau

W

F

Feb 1888

12

S

WA

SC

OR

At School

9

Y

Y

Y

____ Walter A

Son

W

M

Sep 1892

8

S

WA

SC

OR

5a.  1910 Census Index/Images (online at Genealogy.com, Image #3 of 16 — indexed "Dimysino M. Holt"):  Mesa Pct., Franklin Co., WA, Roll 1656 (Book 1), p. 125A, SN ?A, SD 3, ED 59, enumerated 25 Apr 1910, official enumeration date 15 Apr 1910 (extracted by Diana Gale Matthiesen):

1910:  for an explanation of the column headings, please see What the Numbers in the Federal Census Mean (missing columns contained no data).
1	2	3	4	5	6	7	8	9	12	13	14	17	18	19	20	23	24	26	27	28	29
51	52	Holt Dionysius M	Head	M	W	55	M1	28	SC	NC	SC	Eng	Farmer	General Farm	OA	Y	Y	O	F	F	52

5b.  1910 Census Index/Images (online at Genealogy.com, Image #7 of 24):  1709 Opal Street, Pullman (Ward 3), Whitman Co., WA, Roll 1674 (Book 2), p. 275A, SN 4A, SD 3, ED 271, enumerated 20 Apr 1910, official enumeration date 15 Apr 1910 (extracted by Diana Gale Matthiesen):

1910:  for an explanation of the column headings, please see What the Numbers in the Federal Census Mean (missing columns contained no data).
		1	2	3	4	5	6	7	8	9	10	11	12	13	14	17	18	19	20	21	22	23	24	25	26	28
*	1709	71	71	Holt Nancy H	Head	F	W	47	M1	34	5	5	OR	MO	MO	Eng	Dressmaker	at Home	OA	N	0	Y	Y		R	H
				____ Walter A	Son	M	W	18	S				WA	SC	OR	Eng	None					?	?	Y
				Packingham Mary	Roomer	F	W	28	S				IL	IL	MA	Eng	Nurse Reg	Professional	W	N	0	Y	Y
*Opal Street

6.  1920 Census Index/Images (online at Ancestry.com):  can't find either Dionysius or Nancy, at least they're not indexed in a way that I've been able to pull them up.

7.  Oregon Death Index, 1903-98 (online at Ancestry.com):

Name	County	Death Date	Certificate
Holt, Dionysius Melville	Clackamas	09 Apr 1928	135

This may or may not be our subject, but the name isn't exactly common.  Ordering the certificate would provide the answer. 

8.  Archives of the WAWHITMA-L mailing list (online at RootsWeb.com).  Excerpt from an index to Judith Crithfield's book, Of Yesterday and the River (1964/1973. Self-published, C.W. Hill Print Co., Spokane, WA):

... Holt 10 Dionysius Holt 30 James B. Holt 25 Nish Holt 31, 96 ...